5,523 research outputs found
H infinity observer for time-delay systems. Application to FDI for irrigation canals
This paper deals with the problem of fault detection and isolation for time-varying delayed systems. It consists to develop a observer that generates residuals sensitive to some faults and insensitive to others in order to detect and isolate actuator faults which can occur on the regulation gates of an irrigation canal. The observer design uses a simplified approximate model of the Saint-Venant equations and is formulated with delay-dependent Linear Matrix Inequality (LMI). Simulations done with a realistic model of a real canal show the effectiveness of the metho
Wide-field Infrared Survey Explorer Observations of the Evolution of Massive Star-forming Regions
We present the results of a mid-infrared survey of 11 outer Galaxy massive star-forming regions and 3 open clusters with data from the Wide-field Infrared Survey Explorer (WISE). Using a newly developed photometric scheme to identify young stellar objects and exclude extragalactic contamination, we have studied the distribution of young stars within each region. These data tend to support the hypothesis that latter generations may be triggered by the interaction of winds and radiation from the first burst of massive star formation with the molecular cloud material leftover from that earlier generation of stars. We dub this process the "fireworks hypothesis" since star formation by this mechanism would proceed rapidly and resemble a burst of fireworks. We have also analyzed small cutout WISE images of the structures around the edges of these massive star-forming regions. We observe large (1-3 pc size) pillar and trunk-like structures of diffuse emission nebulosity tracing excited polycyclic aromatic hydrocarbon molecules and small dust grains at the perimeter of the massive star-forming regions. These structures contain small clusters of emerging Class I and Class II sources, but some are forming only a single to a few new stars
ATLASGAL-selected massive clumps in the inner Galaxy: VI. Kinetic temperature and spatial density measured with formaldehyde
We aim to directly determine the kinetic temperature and spatial density with
formaldehyde for the 100 brightest ATLASGAL-selected clumps at 870 m
representing various evolutionary stages of high-mass star formation. Ten
transitions ( = 3-2 and 4-3) of ortho- and para-HCO near 211, 218, 225,
and 291 GHz were observed with the APEX 12 m telescope. Using non-LTE models
with RADEX, we derive the gas kinetic temperature and spatial density using the
measured p-HCO 3-2/3-2,
4-3/4-3, and 4-3/3-2
ratios. The gas kinetic temperatures derived from the p-HCO
3-2/3-2 and 4-3/4-3
line ratios are high, ranging from 43 to 300 K with an unweighted average of
91 4 K. Deduced values from the = 3-2 and 4-3
transitions are similar. Spatial densities of the gas derived from the
p-HCO 4-3/3-2 line ratios yield 0.6-8.3
10 cm with an unweighted average of 1.5 (0.1)
10 cm. A comparison of kinetic temperatures derived from p-HCO,
NH, and the dust emission indicates that p-HCO traces a distinctly
higher temperature than the NH (2,2)/(1,1) transitions and the dust,
tracing heated gas more directly associated with the star formation process.
The HCO linewidths are found to be correlated with bolometric luminosity
and increase with the evolutionary stage of the clumps, which suggests that
higher luminosities tend to be associated with a more turbulent molecular
medium. It seems that the spatial densities measured with HCO do not vary
significantly with the evolutionary stage of the clumps. However, averaged gas
kinetic temperatures derived from HCO increase with time through the
evolution of the clumps.Comment: Accepted for publication in A&
Dusty Cometary Globules in W5
We report the discovery of four dusty cometary tails around low mass stars in
two young clusters belonging to the W5 star forming region. Fits to the
observed emission profiles from 24 micron observations with the Spitzer Space
Telescope give tail lifetimes < 30 Myr, but more likely < 5 Myr. This result
suggests that the cometary phase is a short lived phenomenon, occurring after
photoevaporation by a nearby O star has removed gas from the outer disk of a
young low mass star (see also Balog et al. 2006; Balog et al. 2008).Comment: 11 pages, 3 figures. Accepted for publication to ApJ Letter
Efficient exploration of unknown indoor environments using a team of mobile robots
Whenever multiple robots have to solve a common task, they need to coordinate their actions to carry out the task efficiently and to avoid interferences between individual robots. This is especially the case when considering the problem of exploring an unknown environment with a team of mobile robots. To achieve efficient terrain coverage with the sensors of the robots, one first needs to identify unknown areas in the environment. Second, one has to assign target locations to the individual robots so that they gather new and relevant information about the environment with their sensors. This assignment should lead to a distribution of the robots over the environment in a way that they avoid redundant work and do not interfere with each other by, for example, blocking their paths. In this paper, we address the problem of efficiently coordinating a large team of mobile robots. To better distribute the robots over the environment and to avoid redundant work, we take into account the type of place a potential target is located in (e.g., a corridor or a room). This knowledge allows us to improve the distribution of robots over the environment compared to approaches lacking this capability. To autonomously determine the type of a place, we apply a classifier learned using the AdaBoost algorithm. The resulting classifier takes laser range data as input and is able to classify the current location with high accuracy. We additionally use a hidden Markov model to consider the spatial dependencies between nearby locations. Our approach to incorporate the information about the type of places in the assignment process has been implemented and tested in different environments. The experiments illustrate that our system effectively distributes the robots over the environment and allows them to accomplish their mission faster compared to approaches that ignore the place labels
Constraining the Nature of the Galactic Center X-ray Source Population
We searched for infrared counterparts to the cluster of X-ray point sources
discovered by Chandra in the Galactic Center Region (GCR). While the sources
could be white dwarfs, neutron stars, or black holes accreting from stellar
companions, their X-ray properties are consistent with magnetic Cataclysmic
Variables, or High Mass X-ray Binaries (HMXB) at low accretion-rates. A direct
way to decide between these possibilities and hence between alternative
formation scenarios is to measure or constrain the luminosity distribution of
the companions. Using infrared (J, H, K, Br-gamma) imaging, we searched for
counterparts corresponding to typical HMXB secondaries: spectral type B0V with
K<15 at the GCR. We found no significant excess of bright stars in Chandra
error circles, indicating that HMXBs are not the dominant X-ray source
population, and account for fewer than 10% of the hardest X-ray sources.Comment: 4 pages, 3 figures, 1 table, accepted in ApJ Letters for publicatio
A Quantum-Proof Non-Malleable Extractor, With Application to Privacy Amplification against Active Quantum Adversaries
In privacy amplification, two mutually trusted parties aim to amplify the
secrecy of an initial shared secret in order to establish a shared private
key by exchanging messages over an insecure communication channel. If the
channel is authenticated the task can be solved in a single round of
communication using a strong randomness extractor; choosing a quantum-proof
extractor allows one to establish security against quantum adversaries.
In the case that the channel is not authenticated, Dodis and Wichs (STOC'09)
showed that the problem can be solved in two rounds of communication using a
non-malleable extractor, a stronger pseudo-random construction than a strong
extractor.
We give the first construction of a non-malleable extractor that is secure
against quantum adversaries. The extractor is based on a construction by Li
(FOCS'12), and is able to extract from source of min-entropy rates larger than
. Combining this construction with a quantum-proof variant of the
reduction of Dodis and Wichs, shown by Cohen and Vidick (unpublished), we
obtain the first privacy amplification protocol secure against active quantum
adversaries
Application of B-splines to determining eigen-spectrum of Feshbach molecules
The B-spline basis set method is applied to determining the rovibrational
eigen-spectrum of diatomic molecules. A particular attention is paid to a
challenging numerical task of an accurate and efficient description of the
vibrational levels near the dissociation limit (halo-state and Feshbach
molecules). Advantages of using B-splines are highlighted by comparing the
performance of the method with that of the commonly-used discrete variable
representation (DVR) approach. Several model cases, including the Morse
potential and realistic potentials with 1/R^3 and 1/R^6 long-range dependence
of the internuclear separation are studied. We find that the B-spline method is
superior to the DVR approach and it is robust enough to properly describe the
Feshbach molecules. The developed numerical method is applied to studying the
universal relation of the energy of the last bound state to the scattering
length. We numerically illustrate the validity of the quantum-defect-theoretic
formulation of such a relation for a 1/R^6 potential.Comment: submitted to can j phys: Walter Johnson symposu
Ultrathin Oxide Films by Atomic Layer Deposition on Graphene
In this paper, a method is presented to create and characterize mechanically
robust, free standing, ultrathin, oxide films with controlled, nanometer-scale
thickness using Atomic Layer Deposition (ALD) on graphene. Aluminum oxide films
were deposited onto suspended graphene membranes using ALD. Subsequent etching
of the graphene left pure aluminum oxide films only a few atoms in thickness. A
pressurized blister test was used to determine that these ultrathin films have
a Young's modulus of 154 \pm 13 GPa. This Young's modulus is comparable to much
thicker alumina ALD films. This behavior indicates that these ultrathin
two-dimensional films have excellent mechanical integrity. The films are also
impermeable to standard gases suggesting they are pinhole-free. These
continuous ultrathin films are expected to enable new applications in fields
such as thin film coatings, membranes and flexible electronics.Comment: Nano Letters (just accepted
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